The release of gravitational energy from the accretion of matter onto a
black hole still is a mystery. Observationally, the thermal radiadion from
an inner accretion disk and its high energy tail are manifestations of
processes in the inner region, while the ejection of radio jets demonstrates
the energy and plasma outflow on larger scales. Models include
materialisation of energy from the central source in the form of pair
creation within a region of high density that is opaque to all kinds of
radiation. At some point leptons may escape the dense inner regions, and
annihilation of positrons in nearby components such as the corona and
accretion disk could be expected. Transient line features have been reported
from two sources before, and tentatively associated with positron
annihilation. Flaring of the microquasar V404 Cygni in June-July 2015
allowed to test this model again. With SPI on INTEGRAL, which has
demonstrated excellent measurement capability for positron annihilation in
the Galaxy, we now find characteristic signatures of the annihilation of
positrons across the 200-1000 keV energy range during this flaring phase. We
discuss details of the positron annihilation spectra, and what they might
tell us about pair plasma in the central energy source of microquasars.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2016.APR.M13.9